Lubricating composition



3,189,545 LUBRICATING COMPOSITION Randel Q. Little, Jr., and Sigmund S. Deluga, both of Munster, Ind., assignors to Standard Oil Company, Chicago, lll., a corporation of Indiana No Drawing. Filed Oct. 30, 1961, Ser. No. 148,749 6 Claims. (Cl. 252-46.6)

This invention relates to internal combustion engine lubricating oils and more particularly to lubricating compositions for use in compression ignition engines having silver-containing parts in frictional contact with other metal parts. The invention provides lubricating compositions characterized by inhibiting silver wear caused by the presence of corrosive sulfur in the lubricating oil, and improved lubricity properties.

Organic compounds containing active sulfur are often used in lubricating oils because of their excellence in preventing oxidative deterioration of the oil under conditions of use, and/or to impart desirable extreme pressure (EP) properties. However, when lubricating oils containing such organic compounds are used in the presence of silver parts in frictional contact with other parts, e.g. in compression ignition internal combustion engines where silver plated bearings are present, typically as in electrical generating and railway diesel engines, they normally tend to promote excessive wear of such silver-containing parts due to the presence of corrosive sulfur. Undue wear of silver and copper and especially silver-on-steel wear is detrimental to the engine and increases the frequency of replacing certain engine parts. However, in view of the excellence of certain sulfur-containing organic compounds as oxidation inhibitors, it is not desirable to eliminate such sulfur compounds from the lubricating oil or replace them with less effective agents. Thusv it is desirable to counteract the adverse effect of corrosive sulfur on parts containing silver and to decrease the extent of wear.

The lubricating composition claimed herein comprises a major amount of a lubricating oil containing corrosive sulfur in an amount sufficient to normally tend to cause silver-on-steel seizure and wear, and a small amount of a sulfur corrosion inhibitor comprising 1 or more dialkyl pentaerythritol diphosphites.

The dialkyl pentaerythritol diphosphites referred to herein have a composition corresponding to the structural formula wherein R and R are alkyi radicals having from about 1 to about carbon atoms per radical. A means of preparing such dialkyl diphosphites is described by Gould et al. in U.S. Patent No. 2,961,454. Such dialkyl pentacrythritol diphosphites must be characterized by acceptable oil solubility properties in order to be used in our composition, and accordingly, the sum of the carbon atoms in the alkyl radicals should be more than about 7, although the individual alkyl radicals mayhave from about 1 to 20 carbon atoms, and preferably 8 to 16 carbon atoms. C C alkyl radicals are advantageously used in the diphosphite to be used in compounding our lubricating composition. Illustrative alkyl radicals are the methyl, propyl, n-butyl. amyl. hexyl, octyl, decyl, lauryl, palmityl, stearyl, and branched chain alkyls, such as isobutyl, tert.-butyl, neo-pentyl, Z-ethyl hexyl, oxo-octyl, 2,9-dimethyl decyl, and others.

According to the preparation described in U.S. Patent No. 2,961,454, the dialkyl esters may be prepared by trans-esterifying 2 mols of tris 2-chlorpropyl or tris 2- 3,18%,545 Patented June 15, 1965 chlorbutyl phosphite with 1 mol of pentaerythritol, and thereafter trans-esterifying the resulting product with 2 mols of an alkanol to produce the corresponding dialkyl pentaerythritol diphosphite having the structural formula referred to above. Mixtures of alkanols may be used in the trans-esterification, in which event the resulting product will be a mixture of diphosphites wherein the R and R radicals on any particular molecule will be the same or different, e.g., from trans-esterification with hexanol and octanol, the product diphosphites will be of the C -C C -C and C -C species.

Didecyl pentaery-thritol diphosphite is a typical example of a compound suitable for use in compounding the lubricating compositions and concentrates claimed herein. A preparation of that diphosphite is illustrated by Examples 19 and 20, taken in light of the procedure of Example 1 of U.S. Patent No. 2,961,454.

The amount of diphosphite used is in the range of about ,1 to about 5 weight percent based, as are all composition figures used herein, on the weight of the total lubricating composition, and is advantageously in the range of about /4 to about 2 weight percent. For a given extent of effectiveness, somewhat greater weight percentages of the higher molecular weight diphosphites are required than for lower molecular weight diphosphites.

Examples of sulfur-containing antioxidants which may cause or promote undue corrosivity of silver-containing parts due to corrosive sulfur, and in combination with which the diphosphites herein described are useful, are: the sulfurized terpenes (e.g. sulfurized dipentene), sulfurized olefin polymers (e.g. sulfurized isobutylene), sul furized petroleum waxes, sulfochlorinated polymers, hydrocarbon sulfides (e.g. benzyl disulfide), etc. Also useable are such oxidation inhibitors as dithienyl methane, dithienyl ethane, dithienyl propane, o-hydroxy dithienyl methane, 3-thienylthioethers, products from the reaction of bicyclic terpene with P 5 and elemental sulfur, other phosphorus pentasulfide-terpene reaction products alone or in admixture with other antioxidants such as a 2,4,6 trialkyl phenol or a 2,2'-alkylindcne-bis(4-alkyl-6-tetraalkyl phenol), reaction products of thiophenethiol with alcohol or thiophenethiol and a phosphorus halide, reaction products or diphenylamine and trithioaeetone, etc. Other sulfur-containing oxidation inhibitors will be evident to those having ordinary skill in the art.

The lubricating compositions of our invention can readily be formulated from a concentrate, e.g., a combination of from about 5 to preferably 20-50%, of a sulfur corrosion inhibitor and lubricity improver comprising one or more dialkyl pentaerythritol diphosphites in a suitable solvent. Although other solvents will be evident to those having ordinary skill in the art, it is preferred that the concentrate be prepared using a lubricating oil, e.g., a mineral lubricating oil, or other lubricating oil as more fully described hereinbelow as the solvent. In addition to the sulfur corrosion inhibitor and a sulfur-containing antioxidant, as referred to above, other addition agents may be present in the concentrate. Such other addition agents include anti-rust agents, detergents, alkaline agents, extreme pressure agents, pour point depressors, antit'oaming agents, and other well-known additives.

In order to test the effectiveness of addition agents of this invention in the prevention of silver-on-steel wear, tests were conducted in accordance with the Modified Electromotive Division (EMD) Test, and on the Kinetic Oiliness Testing Machine.

The Modified EMD Test is designed to determine silver and copper corrosion and wear inhibiting properties of addition agents. In this test weighed freshly polished x 2" x silver strips and l" x 2" x A copper strips are immersed in 300 grams of the test sample, stirred at 300 r.p.m., at 285 F. for 72 hours. At the end of the test period, the strips are removed, and cleaned electrolytically in 5% KOH to remove deposits, dried and weighed. The degree of corrosion is measured by determining the milligram weight loss of the test strips. The test was also run at 325 F.

The Kinetic Oiliness Testing Machine (KOTM) essentially consists of two small rotatable concentric circular steel rails spaced about 4-inch apart having three smaller circular silver rails riding thereon. The silver rails are attached to an assembly which is connected to a torque spring and gauge to measure relative friction. The silver rails are spaced so as to be equidistant apart around the circumference of the steel rails when the assembly is' superimposed on the steel rails. The silver rails are large enough to contact each steel rail in two places, giving four silver-on-steel contacts for each silver rail. Load on the contacting surfaces is increased by adding weights to the silver rail assembly. In the test procedure, the steel rails are rotated at 2 rpm. in contact with the silver rails while lubricating with the sample oil undergoing test and the oil temperature is maintained constant at 350 F. while increasing the load to 34 pounds. The temperature is then raised while taking relative friction readings until the temperature of incipient seizure is reached. Relative friction is a value varying directly with the friction between the surfaces as detected by torque increase in the silver-rail assembly. The temperature of incipient seizure is the temperature at which relative friction begins to increase markedly more rapidly. The temperature of incipient seizure and the relative friction at that temperature are noted as test result values, and are indicative of the lubricity properties of the lubricant.

The tests according to the KOTM procedure are particularly useful as tests for silver-on-steel wear for use in formulating lubricating oils especially for compression ignition internal combustion engines such as diesel engines used in generating electrical power, including railway diesel engines, for determining wear of silver-containing engine parts such as are present in wrist pin assemblies or such as may be present in engine bearings.

The Modified EMD and KOTM Tests were run on samples containing didecyl pentaerythritol diphosphite in the amounts set forth in Table I. The base oil was a mineral lubricating oil of SAE 40 grade having a viscosity index of 63 and an SSU viscosity at 210 F. of 78, and containing 6% detergent-type additive and 0.5% sulfurized dipentene oxidation inhibitor. The sulfurized dipentene was the source of corrosive sulfur. The results of the The foregoing data highlight not only the significant extent of the reduction by our'c'laimed lubricating composition of the corrosion of silver, and also of copper, de-

spite the presence of corrosive sulfur, but further point up the simultaneous improvement in lubricity characteristics of the composition. It is evident that We have provided lubrjca't'in'g compositions Icapabller of cornhattirtg the .c ora hydrocarbon mineral lubricating oil, a sulfur-containing anti-oxidant in amounts sufficient to normally tend to cause silver-on-steel seizure and wear due to the presence of said anti-oxidant: and from to 5% of a sulfur corrosion inhibitor comprising a d-ialkyl pentaerythritol diphosphite having a composition corresponding to the structural formula:

wherein R and R are alkyl radicals containing from about 1 to-about carbon atoms per radical, and wherein the sum of the carbon atoms in said radicals is more than about 7.

2. The composition of claim 1 wherein said corrosive sulfur comprises from about to about 2 weight percent of a sulfurized terpene and said dialkyl pentaerythritol diphosphite comprises from about to about 5 weight percent.

3. The composition of claim 1 wherein said alkyl radicals have from about 8 to 18 carbon atoms per radical.

4. The composition of claim 1 wherein radical R has a different number of carbon atoms than has radical R 5. The composition of claim 1 wherein said diphosphite comprises from about A to 2 weight percent of didecyl pentaerythritol diphosphite.

6. A lubricant concentrate comprising from about 5 to about 75 weight percent of a dialkyl pentaerythritol diphosphite having a composition corresponding to the structural formula:

O-GH:

wherein R and R are alkyl radicals having from about 1 to about 20 carbon atoms per radical, and wherein the sum of the carbon atoms in said radicals is more than about 7, a sulfur-containing anti-oxidant, and an amount of mineral lubricating oil sufiicient to solubil-ize said diphosphite, said concentrate being capable of dilution with mineral lubricating oil to a concentration of said diphosphite in the range of from to about 5 weight percent.

References Cited by the Examiner UNITED STATES PATENTS Denison; OX s a tibh'ofvLubr-icating one: Indrand'Eng.

Chem.,'volu'me '36, M44, New 7 New Product Report (NPR-"1759;, Weston Chemical Corp..(3 pages), May. 1-6-, 19.60.

DANIEILE'. WYMAN, Prima'ry Examiner.

' u'uus GREEhgWAED, x miner, 

1. A LUBRICATING COMPOSITION CHARACTERIZED BY IMPROVED RESISTANCE TO SULFUR CORROSION AND IMPROVED LUBRICITY PROPERTIES, WHICH COMPOSITION COMPRISES A MAJOR AMOUNT OF A HYDROCARBON MINERAL LUBRICATING OIL, A SULFUR-CONTAINING ANTI-OXIDANT IN AMOUNTS SUFFICIENT TO NORMALLY TEND TO CAUSE SILVER-ON-STEEL SEIZURE AND WEAR DUE TO THE PRESENCE OF SAID ANTI-OXIDANT, AND FROM 1/10 TO 5% OF A SULFUR CORROSION INHIBITOR COMPRISING A DIALKYL PENTAERYTHRITOL DIPHOSPHITE HAVING A COMPOSITION CORRESPONDING TO THE STRUCTURAL FORMULA: 